U.S. patent number 7,717,098 [Application Number 12/461,897] was granted by the patent office on 2010-05-18 for controller of internal combustion engine.
This patent grant is currently assigned to Denso Corporation. Invention is credited to Tomoaki Nakano, Hideki Suzuki.
United States Patent |
7,717,098 |
Nakano , et al. |
May 18, 2010 |
Controller of internal combustion engine
Abstract
An engine controller performs low opening degree control during
a first intake stroke period since an engine start is commenced
until first intake strokes of respective cylinders end. Thus, an
opening degree of an intake throttle valve is controlled to a fully
closed position or proximity of the fully closed position such that
intake pressure downstream of the intake throttle valve becomes
equal to or lower than critical pressure with respect to intake
pressure upstream of the intake throttle valve during an intake
stroke of each cylinder. The controller calculates a leak air
quantity at the time when the intake throttle valve is fully closed
based on an intake air quantity sensed during the low opening
degree control. The controller corrects a feedback gain of idle
speed control in accordance with the leak air quantity of the
intake throttle valve.
Inventors: |
Nakano; Tomoaki (Toyota,
JP), Suzuki; Hideki (Chita-gun, JP) |
Assignee: |
Denso Corporation (Kariya,
JP)
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Family
ID: |
39319110 |
Appl.
No.: |
12/461,897 |
Filed: |
August 27, 2009 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090314254 A1 |
Dec 24, 2009 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11907448 |
Oct 12, 2007 |
7597087 |
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Foreign Application Priority Data
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Oct 20, 2006 [JP] |
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2006-286114 |
Oct 20, 2006 [JP] |
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2006-286115 |
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Current U.S.
Class: |
123/568.14;
123/480 |
Current CPC
Class: |
F02D
31/005 (20130101); F02D 31/002 (20130101) |
Current International
Class: |
F02M
25/07 (20060101); F02M 51/00 (20060101) |
Field of
Search: |
;123/568.11,568.14,403,405,479,480 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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05-288101 |
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Nov 1993 |
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JP |
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2536242 |
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Jul 1996 |
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JP |
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09-170474 |
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Jun 1997 |
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JP |
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Primary Examiner: Kwon; John T
Attorney, Agent or Firm: Nixon & Vanderhye PC
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application is a Division of application Ser. No. 11/907,448,
filed Oct. 12, 2007, the entire contents of which are hereby
incorporated by reference into this application. This application
is also based on and claims priority from Japanese Patent
Applications No. 2006-286114 filed on Oct. 20, 2006 and No.
2006-286115 filed on Oct. 20, 2006, the contents are hereby
incorporated by reference into this application.
Claims
What is claimed is:
1. A controller of an internal combustion engine having intake
throttle valves in branch intake passages of respective cylinders
for regulating intake air quantities, the branch intake passages
branching from a main intake passage of the engine for introducing
the intake air into the respective cylinders, the controller
comprising: an intake air quantity sensor provided in the main
intake passage for sensing the intake air quantity; a low opening
degree control device that performs low opening degree control for
controlling an opening degree of the intake throttle valve during
fuel cut control for stopping fuel injection of the engine such
that intake pressure downstream of the intake throttle valve
becomes pressure that is equal to or lower than predetermined
critical pressure with respect to intake pressure upstream of the
intake throttle valve and that does not cause oil loss via valve
guides during the intake stroke of each cylinder; a leak air
quantity calculation device that calculates a leak air quantity at
the time when the intake throttle valve is fully closed based on
the intake air quantity sensed with the intake air quantity sensor
during the low opening degree control; and an intake throttle valve
opening degree correction device that corrects the opening degree
of the intake throttle valve in accordance with the leak air
quantity.
2. The controller as in claim 1, further comprising: an idle speed
control device that performs idle speed control for performing
feedback control of the opening degree of the intake throttle valve
such that actual rotation speed of the engine coincides with target
idle speed during idle operation of the engine, wherein the intake
throttle valve opening degree correction device corrects a feedback
gain of the idle speed control in accordance with the leak air
quantity during the idle speed control.
3. A controller of an internal combustion engine having intake
throttle valves in intake passages of respective cylinders of the
engine for regulating intake air quantities, the intake throttle
valve having a function to generate an airflow for equalizing a
fuel-air mixture, the controller comprising: an exhaust gas
recirculation adjustment device that adjusts an exhaust gas
recirculation quantity of the engine; an exhaust gas recirculation
increase control device that performs exhaust gas recirculation
increase control for controlling the exhaust gas recirculation
adjustment device such that the exhaust gas recirculation quantity
increases during low load operation of the engine; an each cylinder
leak air quantity information sensing device that senses a
combustion state in each cylinder during the exhaust gas
recirculation increase control as information about a leak air
quantity at the time when the intake throttle valve of each
cylinder is fully closed; a large leak air cylinder determination
device that determines a cylinder causing a large leak air quantity
of the intake throttle valve to be a large leak air cylinder based
on the combustion state of each cylinder sensed with the each
cylinder leak air quantity information sensing device; and an each
cylinder intake throttle valve opening degree correction device
that corrects an opening degree of the intake throttle valve during
a period corresponding to an intake stroke of the large leak air
cylinder in accordance with the combustion state in the large leak
air cylinder.
4. The controller as in claim 3, wherein the each cylinder leak air
quantity information sensing device senses a rotation fluctuation
of the engine due to the combustion in each cylinder as a parameter
for evaluating the combustion state in each cylinder; and the large
leak air cylinder determination device determines the cylinder
causing the unstable combustion state to be the large leak air
cylinder based on the rotation fluctuation due to the combustion in
each cylinder.
5. The controller as in claim 4, wherein the each cylinder leak air
quantity information sensing device senses the rotation fluctuation
due to the combustion in each cylinder by comparing rotation speed
of the engine corresponding to a combustion stroke of the cylinder
with average rotation speed of all the cylinders, and the large
leak air cylinder determination device determines the cylinder
causing the largest rotation fluctuation amount toward lower
rotation speed from the average rotation speed to be the large leak
air cylinder.
6. The controller as in claim 5, wherein the large leak air
cylinder determination device determines the cylinder causing the
largest rotation fluctuation amount that is directed toward lower
rotation speed from the average rotation speed and that is equal to
or greater than a predetermined value to be the large leak air
cylinder.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a controller of an internal
combustion engine having intake throttle valves in intake passages
of respective cylinders of the engine for adjusting intake air
quantities.
2. Description of Related Art
There has been a system having a throttle valve in an intake pipe
upstream of intake manifolds of respective cylinders (i.e., in
intake pipe collection part upstream of position where intake pipe
branches into intake manifolds of cylinders) of an internal
combustion engine for adjusting an intake air quantity and a bypass
air quantity regulating valve (i.e., idle speed control valve) for
adjusting a bypass air quantity flowing through a bypass passage
bypassing the throttle valve to control idle speed. In such the
system, there is a possibility that a leak air quantity of the
throttle valve (air quantity passing through small gap between
throttle valve and inner wall surface of intake passage when
throttle valve is fully closed) varies due to manufacture
tolerance, an aging change or the like and the controllability of
the idle speed control decreases.
As a countermeasure, a device described in patent document 1
(JP-A-H5-288101) performs fuel cut control when the throttle valve
is fully closed and rotation speed of the engine is equal to or
higher than a predetermined value and calculates the leak air
quantity of the throttle valve based on an intake air quantity
sensed with an airflow meter while the bypass air quantity
regulating valve is fully closed during the fuel cut control (i.e.,
while throttle valve is fully closed). The device controls the
bypass air quantity regulating valve with the use of the leak air
quantity during the idle operation.
When a device described in patent document 2 (JP-A-H9-170474)
performs feedback control of the bypass air quantity regulating
valve to conform actual rotation speed to target idle speed during
the idle operation of the engine, the device estimates an external
load of the engine and subtracts a control amount corresponding to
the external load from a feedback correction amount. Thus, the
device obtains and learns a value corresponding to a change of the
leak air quantity of the throttle valve and corrects the feedback
correction amount by using the learning value.
The applicants of the present application are currently studying a
system having intake throttle valves in intake manifolds of
respective cylinders of an internal combustion engine for adjusting
intake air quantities. In such the system, as shown in FIG. 3,
specifically in an area of a low opening degree Thr of the intake
throttle valve (for example, in idle operation area), the quantity
Gath of the passing air of the intake throttle valve increases and
the intake air quantity increases as the leak air quantity Qleak of
the intake throttle valve (air quantity passing through gap between
intake throttle valve and inner wall surface of intake passage when
intake throttle valve is fully closed) increases even when the
opening degree Thr of the intake throttle valve is the same.
Accordingly, there is a possibility that the rotation of the engine
rises during the idle operation.
If the leak air quantity Qleak of the intake throttle valve
decreases, the passing air quantity Gath of the intake throttle
valve decreases and the intake air quantity decreases even when the
opening degree Thr of the intake throttle valve is the same.
Therefore, there is a possibility that the rotation of the engine
falls.
Moreover, if the leak air quantity Qleak of the intake throttle
valve changes, the relationship between the opening degree Thr of
the intake throttle valve and the passing air quantity Gath (i.e.,
change characteristic of passing air quantity Gath with respect to
opening degree Thr of intake throttle valve) changes. Therefore,
there occurs a problem that the control accuracy of the intake air
quantity by the opening degree control of the intake throttle valve
lowers.
A following problem will occur if the leak air quantity of the
intake throttle valve is calculated based on the intake air
quantity sensed with the airflow meter while the intake throttle
valve is fully closed during the fuel cut control by using the
technology of the patent document 1 in the system having the intake
throttle valves in the intake manifolds of the respective cylinders
of the engine. That is, the capacity of the intake passage
downstream of the intake throttle valve is small in the system
having the intake throttle valves in the intake manifolds of the
respective cylinders of the engine. Therefore, if the intake
throttle valve is fully closed during the fuel cut control (i.e.,
when rotation speed of engine is equal to or higher than fuel cut
resuming rotation speed), intake air pressure downstream of the
intake throttle valve declines greatly. As a result, there is a
possibility that oil loss via valve guides (i.e., phenomenon that
oil lubricating sliding parts of intake valve or the like leaks
toward intake port and is suctioned into intake port) occurs and
the combustion state and the emission of the engine worsen.
When the feedback control of the intake throttle valve is performed
to conform the actual rotation speed to the target idle speed
during the idle operation of the engine with the use of the
technology of the patent document 2 in the system having the intake
throttle valves in the intake manifolds of the respective cylinders
of the engine, a method of calculating a value corresponding to the
leak air quantity of the intake throttle valve by estimating the
external load of the engine and by removing the control amount
corresponding to the external load from the feedback correction
amount could be employed. However, it is difficult to estimate the
external load of the engine with high accuracy. Therefore, the
method of calculating the leak air quantity of the intake throttle
valve based on the feedback correction amount and the external load
has a defect that the leak air quantity of the intake throttle
valve cannot be calculated with high accuracy due to an estimation
error of the external load.
A system described in patent document 3 (Japanese Patent Gazette
No. 2536242) has shutoff valves (i.e., throttle valves) in intake
passages of respective cylinders of an internal combustion engine
for adjusting intake air quantities respectively and bypass
passages bypassing the shutoff valves. The system has control
valves (i.e., idle speed control valves) in the bypass passages of
the respective cylinders for opening/closing the bypass passages
respectively. During the idle operation period, the system fully
closes the shutoff valves provided in the intake passages of the
respective cylinders and controls valve opening periods of the
control valves provided in the bypass passages of the cylinders.
Thus, the system adjusts the intake air quantities and the idle
speed.
In such the system, even if the valve opening periods of the
control valves provided in the bypass passages of the respective
cylinders are equalized during the idle operation, a variation is
caused among the intake air quantities of the cylinders if the leak
air quantities of the shutoff valves provided in the intake
passages of the cylinders (air quantities passing through small
gaps between shutoff valves and intake passage inner walls when
shutoff valves are fully closed) vary among the cylinders due to
manufacture tolerances, aging changes, and the like. Therefore,
there is a possibility that torque of the respective cylinders
varies and the idle speed fluctuate largely.
As a countermeasure, a technology described in the patent document
3 senses the rotation speed as of expansion strokes of the
respective cylinders during the idle operation and calculates
average rotation speed of all the cylinders. The technology
corrects the valve opening period of each control valve provided in
each bypass passage of each cylinder in accordance with a
difference between the rotation speed of the cylinder and the
average rotation speed of all the cylinders.
This technology corrects the valve opening period of each control
valve provided in the bypass passage of each cylinder during the
idle operation, in which the shutoff valve provided in the intake
passage of each cylinder is fully closed. Thus, the technology
corrects the variation among the intake air quantities of the
cylinders due to the variation among the leak air quantities of the
shutoff valves of the respective cylinders or the like during the
idle operation. Therefore, in the operation range, in which the
shutoff valves provided in the intake passages of the cylinders are
opened, the variation among the intake air quantities of the
cylinders due to the variation among the leak air quantities of the
shutoff valves of the cylinders cannot be corrected. Accordingly,
the rotation fluctuation of the engine due to the variation among
the leak air quantities of the shutoff valves of the cylinders
cannot be inhibited.
Moreover, when the technology of the patent document 3 is applied,
installation of the bypass passages to the intake passages of the
respective cylinders and installation of the control valves in the
bypass passages of the respective cylinders are necessary.
Therefore, the system structure will be complicated and the cost
will be increased.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a controller of
an internal combustion engine with a system having intake throttle
valves in intake passages of respective cylinders of the engine
capable of calculating leak air quantities of the intake throttle
valves of the respective cylinders with high accuracy and of
improving controllability of the intake air quantities without
posing adverse effects to operation of the engine.
It is another object of the present invention to provide a
controller of an internal combustion engine with a system having
intake throttle valves in intake passages of respective cylinders
of the engine capable of correcting a variation among intake air
quantities due to a variation among leak air quantities of the
intake throttle valves of the respective cylinders with high
accuracy, suppressing rotation fluctuation of the engine due to the
variation among the leak air quantities of the intake throttle
valves of the respective cylinders and satisfying request for cost
reduction.
According to an aspect of the present invention, a controller of an
internal combustion engine having branch intake passages, which
branch from a main intake passage of the engine and introduce
intake air into respective cylinders, and intake throttle valves in
the branch intake passages of the respective cylinders for
adjusting the intake quantities has an intake air quantity sensor
provided in the main intake passage for sensing the intake air
quantity. The controller has a low opening degree control device
that performs low opening degree control for controlling an opening
degree of the intake throttle valve during a first intake stroke
period since an engine start is commenced until first intake
strokes of the respective cylinders are completed such that intake
pressure downstream of the intake throttle valve becomes pressure
equal to or lower than predetermined critical pressure with respect
to intake pressure upstream of the intake throttle valve during an
intake stroke of each cylinder. The controller has a leak air
quantity calculation device that calculates a leak air quantity at
the time when the intake throttle valve is fully closed based on
the intake air quantity sensed with the intake air quantity sensor
during the low opening degree control. The controller has an intake
throttle valve opening degree correction device that corrects the
opening degree of the intake throttle valve in accordance with the
leak air quantity.
With this structure, the low opening degree control for controlling
the opening degree of the intake throttle valve to the fully closed
position or proximity of the fully closed position is performed so
that the intake pressure downstream of the intake throttle valve
becomes pressure (pressure at which passing air quantity changes in
accordance with opening degree of intake throttle valve without
being affected by pressure difference between pressure upstream of
intake throttle valve and pressure downstream of intake throttle
valve) equal to or lower than the predetermined critical pressure
with respect to the intake pressure upstream of the intake throttle
valve. By sensing the intake air quantity during the low opening
degree control, the passing air quantity corresponding to the
opening degree of the intake throttle valve during the low opening
degree control can be sensed. During the low opening degree
control, the passing air quantity changes in accordance with the
opening degree of the intake throttle valve without being affected
by the pressure difference between the pressure upstream of the
intake throttle valve and the pressure downstream of the intake
throttle valve. Therefore, by using a map or the like beforehand
storing the relationship between the opening degree of the intake
throttle valve and the passing air quantity during the low opening
degree control in the form of data, the leak air quantity as the
passing air quantity at the time when the intake throttle valve is
fully closed can be calculated with high accuracy from the intake
air quantity sensed with the intake air quantity sensor during the
low opening degree control, i.e., the passing air quantity
corresponding to the opening degree of the intake throttle valve
under the low opening degree control.
The air is stored in the intake passage downstream of the intake
throttle valve before the first intake strokes of the cylinders are
completed after the engine start is commenced. Therefore, even if
the low opening degree control for controlling the opening degree
of the intake throttle valve to the fully closed position or the
proximity of the fully closed position is performed during the
first intake stroke period of the cylinders since the engine start
is commenced until the first intake strokes of the respective
cylinders are completed, the air necessary for the combustion in
the engine start can be taken into the cylinders. As a result,
adverse effect on the starting performance of the engine can be
inhibited.
The change of the relationship between the opening degree of the
intake throttle valve and the passing air quantity due to the
change of the leak air quantity of the intake throttle valve
(change characteristic of passing air quantity with respect to
opening degree of intake throttle valve) can be compensated by
correcting the opening degree of the intake throttle valve in
accordance with the calculated leak air quantity of the intake
throttle valve. Accordingly, the controllability of the intake air
quantity through the opening degree control of the intake throttle
valve can be improved without being affected by the aging change of
the leak air quantity of the intake throttle valve and the
like.
Furthermore, the leak air quantity of the intake throttle valve can
be calculated when the engine is started. Therefore, the opening
degree of the intake throttle valve can be corrected in accordance
with the leak air quantity of the intake throttle valve even
immediately after the engine start. Thus, the controllability of
the intake air quantity can be improved even immediately after the
engine start.
According to another aspect of the present invention, the
controller performs low opening degree control for controlling the
opening degree of the intake throttle valve during fuel cut control
for stopping fuel injection of the engine so that the intake
pressure downstream of the intake throttle valve becomes pressure
that is equal to or lower than the predetermined critical pressure
with respect to the intake pressure upstream of the intake throttle
valve and that does not cause oil loss via valve guides in the
intake stroke of each cylinder. The controller calculates a leak
air quantity at the time when the intake throttle valve is fully
closed based on the intake air quantity sensed with the intake air
quantity sensor during the low opening degree control and corrects
the opening degree of the intake throttle valve in accordance with
the leak air quantity.
In the system having the intake throttle valves in the intake
passages of the respective cylinders of the engine, the capacity of
the intake passage downstream of the intake throttle valve is
small. Therefore, if the intake throttle valve is fully closed
during the fuel cut control (i.e., when rotation speed of engine is
equal to or higher than fuel cut resuming rotation speed), there is
a possibility that the intake pressure downstream of the intake
throttle valve declines greatly and the oil loss via the valve
guides occurs. The above-described controller performs the low
opening degree control for controlling the opening degree of the
intake throttle valve to the fully closed position or proximity of
the fully closed position so that the intake pressure downstream of
the intake throttle valve becomes the pressure that is equal to or
lower than the critical pressure with respect to the intake
pressure upstream of the intake throttle valve and that does not
cause the oil loss via the valve guides during the fuel cut
control. The controller calculates the leak air quantity at the
time when the intake throttle valve is fully closed based on the
intake air quantity sensed with the intake air quantity sensor
during the low opening degree control. Thus, the leak air quantity
of the intake throttle valve can be calculated with high accuracy
while inhibiting the oil loss via the valve guides and eventual
deterioration of the combustion state or emission of the
engine.
According to yet another aspect of the present invention, a
controller of an internal combustion engine having intake throttle
valves in intake passages of respective cylinders of the engine for
regulating intake air quantities, each intake throttle valve having
a function to generate an airflow for equalizing a fuel-air
mixture, has an exhaust gas recirculation adjustment device that
adjusts an exhaust gas recirculation quantity of the engine, an
exhaust gas recirculation increase control device that performs
exhaust gas recirculation increase control for controlling the
exhaust gas recirculation adjustment device such that the quantity
of the exhaust gas recirculation increases during low load
operation of the engine, an each cylinder leak air quantity
information sensing device that senses a combustion state in each
cylinder during the exhaust gas recirculation increase control as
information about the leak air quantity at the time when the intake
throttle valve of each cylinder is fully closed, a large leak air
cylinder determination device that determines a cylinder (large
leak air cylinder) causing a large leak air quantity of the intake
throttle valve based on the sensed combustion state in each
cylinder, and an each cylinder intake throttle valve opening degree
correction device that corrects the opening degree of the intake
throttle valve during a period corresponding to an intake stroke of
the large leak air cylinder in accordance with the combustion state
in the large leak air cylinder.
If the leak air quantity of the intake throttle valve increases
when the intake throttle valve has the function to generate the
airflow (e.g., tumble flow or swirl flow) for equalizing the
fuel-air mixture, intensity of the airflow generated by the intake
throttle valve is weakened correspondingly and the effect to
equalize the fuel-air mixture is lowered. Therefore, if the exhaust
gas recirculation quantity (EGR quantity) is increased during the
low load operation of the engine, in which the influence of the EGR
is large, the equalizing effect of the fuel-air mixture is further
lowered by the influence of the EGR and the combustion state
becomes unstable in the cylinder corresponding to the intake
throttle valve with the large leak air quantity.
Paying attention to such the characteristic, the EGR increase
control for controlling the EGR adjustment device to increase the
EGR quantity during the low load operation of the engine is
performed. The combustion states of the respective cylinders are
sensed as information about the leak air quantities of the intake
throttle valves of the respective cylinders during the EGR increase
control, and the cylinder causing the unstable combustion state is
determined based on the combustion states of the respective
cylinders. Thus, the large leak air cylinder (cylinder with large
leak air quantity) can be determined with high accuracy. The
controller corrects the opening degree of the intake throttle valve
during the period corresponding to the intake stroke of the large
leak air cylinder in accordance with the combustion state
(information about leak air quantity) in the large leak air
cylinder. Thus, the opening degree of the intake throttle valve can
be corrected in accordance with the leak air quantity of the intake
throttle valve of the large leak air cylinder. By repeatedly
performing the processing, the variation among the intake air
quantities due to the variation among the leak air quantities of
the intake throttle valves of the respective cylinders can be
corrected with high accuracy, and the rotation fluctuation of the
engine due to the variation among the leak air quantities of the
intake throttle valves of the respective cylinders can be
suppressed.
Moreover, there is no need to provide bypass passages bypassing the
intake throttle valves of the respective cylinders or control
valves for opening/closing the bypass passages of the respective
cylinders. Therefore, the system structure can be simplified and
the cost can be reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
Features and advantages of embodiments will be appreciated, as well
as methods of operation and the function of the related parts, from
a study of the following detailed description, the appended claims,
and the drawings, all of which form a part of this application. In
the drawings:
FIG. 1 is a schematic diagram showing an engine control system
according to a first embodiment of the present invention;
FIG. 2 is a longitudinal cross-sectional view showing an intake
throttle valve unit and a proximity thereof according to the first
embodiment;
FIG. 3 is a diagram showing a relationship between a leak air
quantity and an opening degree of the intake throttle valve;
FIG. 4 is a time chart for explaining a calculation method of the
leak air quantity according to the first embodiment;
FIG. 5 is a diagram showing a pressure range equal to or lower than
critical pressure;
FIG. 6 is a flowchart showing a processing flow of a leak air
quantity calculation program according to the first embodiment;
FIG. 7 is a flowchart showing a processing flow of ISC feedback
correction amount calculation program according to the first
embodiment;
FIG. 8 is a map showing a basic leak air quantity according to the
first embodiment;
FIG. 9 is a map showing a relationship between the opening degree
of the intake throttle valve and a passing air quantity during low
opening degree control according to the first embodiment;
FIG. 10 is a time chart for explaining a calculation method of a
leak air quantity according to a second embodiment of the present
invention;
FIG. 11 is a flowchart showing a processing flow of a leak air
quantity calculation program according to the second
embodiment;
FIG. 12 is a schematic diagram showing an engine control system
according to a third embodiment of the present invention;
FIG. 13 is a time chart for explaining each cylinder intake
throttle valve opening degree correction according to a third
embodiment of the present invention; and
FIG. 14 is a flowchart showing a processing flow of an each
cylinder intake throttle valve opening degree correction program
according to the third embodiment.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
A first embodiment of the present invention will be explained in
reference to FIGS. 1 to 9. First, a schematic structure of an
engine intake system will be explained with reference to FIG. 1. An
engine 11 (for example, inline four-cylinder engine) as an internal
combustion engine has four cylinders of a first cylinder #1 to a
fourth cylinder #4. An airflow meter 23 (intake air quantity
sensor) that senses an intake air quantity is provided in an intake
pipe 12 (main intake passage) of the engine 11. A surge tank 13 is
provided downstream of the airflow meter 23, and intake manifolds
14 (branch intake passages) for introducing air into respective
cylinders of the engine 11 are provided to the surge tank 13.
Intake throttle valve units 15 are attached to the intake manifolds
14 of the respective cylinders, and injectors (not shown) for
injecting fuel are attached near intake ports of the respective
cylinders. Spark plugs (not shown) are attached to a cylinder head
of the engine 11 for the respective cylinders. A fuel air mixture
in the cylinders is ignited with spark discharge from the
respective spark plugs.
A coolant temperature sensor 25 for sensing coolant temperature Tw
and a crank angle sensor 26 for outputting a pulse signal every
time a crankshaft of the engine 11 rotates by a predetermined crank
angle are attached to a cylinder block of the engine 11. A crank
angle CA and engine rotation speed Ne are sensed based on the
output signal of the crank angle sensor 26. An accelerator sensor
27 senses an accelerator operation amount ACCP (depressed amount of
accelerator).
Next, the structure of the intake throttle valve unit 15 will be
explained in reference to FIG. 2. In the intake throttle valve unit
15 of each cylinder, an intake passage 18 with a substantially
quadrangular cross-section is formed in a housing 17 made of a
resin. An intake throttle valve 19 of a cantilever type for opening
and closing the intake passage 18 is provided in the intake passage
18. A shaft 20 as a rotary shaft is attached to a lower end portion
of the intake throttle valve 19 such that the intake throttle valve
19 can rotate about the shaft 20 in an opening direction and a
closing direction. Each intake throttle valve 19 is formed in the
shape that matches with the cross-sectional shape of the intake
passage 18 (i.e., substantially quadrangular shape in the present
embodiment). The cross-sectional shape of the intake passage 18 or
the shape of the intake throttle valve 19 is not limited to the
substantially quadrangular shape. Rather, the cross-sectional shape
or the shape may be any other shape such as substantially a
semicircular shape or substantially a half-elliptical shape.
The intake throttle valves 19 of the respective cylinders are
connected to the common shaft 20 and rotate integrally. A motor 21
(shown in FIG. 1) connected to the shaft 20 is controlled in
accordance with an engine operation condition (accelerator
operation amount ACCP and the like) to control an opening degree
Thr of the intake throttle valves 19 of the cylinders. The opening
degree Thr of the intake throttle valves 19 is sensed with an
intake throttle valve opening degree sensor 29 (shown in FIG.
1).
The intake throttle valve 19 of each cylinder is provided such that
an end (lower end) on the shaft 20 side thereof contacts (or is
located near) an inner wall face of the housing 17 and such that
the intake air can hardly pass under the intake throttle valve 19.
When the intake throttle valve 19 is opened, a flow passage (gap
between intake throttle valve 19 and inner wall face of housing 17)
of the intake air is formed only above the intake throttle valve 19
and a flow passage cross-sectional area above the intake throttle
valve 19 changes in accordance with the opening degree Thr of the
intake throttle valve 19. During low load operation of the engine
11, in which the opening degree Thr of the intake throttle valve 19
becomes comparatively small, an airflow (for example, tumble flow
or swirl flow) for equalizing the fuel-air mixture in the cylinder
can be generated by passing the intake air only through the upper
portion of the intake passage 18 and by increasing flow velocity of
the intake air. An accommodation recess 22 for accommodating the
intake throttle valve 19 when the intake throttle valve 19 is fully
opened is formed in the housing 17 and a neighborhood thereof such
that the intake throttle valve 19 does not hinder the intake air
flow when the intake throttle valve 19 is fully opened.
Outputs of the above-described various sensors are inputted into a
control circuit 28 (ECU). The ECU 28 is constituted mainly by a
microcomputer. The ECU 28 controls a fuel injection quantity of the
injector and ignition timing of the spark plug in accordance with
the engine operation state by executing various kinds of engine
control programs stored in an incorporated ROM (storage
medium).
Furthermore, the ECU 28 calculates a target opening degree of the
intake throttle valve 19 based on the accelerator operation amount
ACCP sensed with the accelerator sensor 27 and the like and
controls the motor 21 of the intake throttle valve 19 to coincide
the actual opening degree Thr of the intake throttle valve 19 with
the target opening degree.
As shown in FIG. 3, specifically in the low opening degree range of
the intake throttle valve 19 (for example, in idle operation
range), if a leak air quantity Qleak of the intake throttle valve
19 increases, a passing air quantity Gath of the intake throttle
valve 19 can increase and the intake air quantity can increase even
when the opening degree Thr of the intake throttle valve 19 is the
same. The leak air quantity Qleak is an air quantity passing
through the gap between the intake throttle valve 19 and the inner
wall face of the intake passage when the intake throttle valve 19
is fully closed. Therefore, there is a possibility that the
rotation of the engine 11 rises during the idle operation. If the
leak air quantity Qleak of the intake throttle valve 19 decreases,
the passing air quantity Gath of the intake throttle valve 19
decreases and the intake air quantity decreases even when the
opening degree Thr of the intake throttle valve 19 is the same.
Therefore, there is a possibility that the rotation of the engine
falls. Moreover, if the leak air quantity Qleak of the intake
throttle valve 19 changes, the relationship between the opening
degree Thr of the intake throttle valve 19 and the passing air
quantity Gath (change characteristic of passing air quantity Gath
with respect to opening degree Thr of intake throttle valve 19)
changes. Accordingly, there is a problem that the control accuracy
of the intake air quantity by the opening degree control of the
intake throttle valve 19 falls.
As a countermeasure, the ECU 28 first executes a leak air quantity
calculation program shown in FIG. 6 to calculate the leak air
quantity Qleak of the intake throttle valve 19 as follows. As shown
in a time chart of FIG. 4, low opening degree control is performed
during a first intake stroke period A since the engine start
(START) is commenced until the first intake strokes of the
cylinders end. The low opening degree control is for controlling
the opening degree Thr of the intake throttle valve 19 to a certain
opening degree for the low opening degree control (fully closed
position or proximity of fully closed position) such that the
pressure downstream of the intake throttle valve 19 becomes
pressure equal to or lower than predetermined critical pressure CP
with respect to the intake pressure upstream of the intake throttle
valve 19, i.e., pressure at which the passing air quantity Gath
changes in accordance with the opening degree Thr of the intake
throttle valve 19 without being affected by the pressure difference
between the pressure upstream of the intake throttle valve 19 and
the pressure downstream of the intake throttle valve 19, during the
intake stroke of each cylinder. In FIG. 4, P#1-P#4 represent the
intake pressure of the first to fourth cylinders #1-#4
respectively, and FL represents a low opening degree control
execution flag. I, C, E1 and E2 represent the intake stroke, a
compression stroke, an expansion stroke and an exhaustion stroke of
each cylinder respectively.
Next, a setting method of the opening degree for the low opening
degree control, i.e., the opening degree at which the intake
pressure downstream of the intake throttle valve 19 becomes the
pressure equal to or lower than the critical pressure CP with
respect to the intake pressure upstream of the intake throttle
valve 19, will be explained. In following Formula (1) of an
orifice, if fcom(Pim/Pamb) becomes constant, the passing air
quantity Gath of the intake throttle valve 19 changes in accordance
with the opening degree (effective flow passage cross-sectional
area Aeff) of the intake throttle valve 19, without being affected
by the pressure difference between the intake pressure Pamb
upstream of the intake throttle valve 19 and the intake pressure
Pim downstream of the intake throttle valve 19. In Formula (1), Cth
represents the flow rate coefficient, R is the gas constant, and T
is intake temperature.
.times..times..times..times..times..function..times..times.
##EQU00001##
Therefore, in the relationship (shown in FIG. 5) between Pim/Pamb
and fcom(Pim/Pamb) defined by following Formulas (2), (3) of an
isentropic flow, a range B shown in FIG. 5 where fcom(Pim/Pamb) is
constant is a range where the intake pressure Pim downstream of the
intake throttle valve 19 becomes the pressure equal to or lower
than the critical pressure CP with respect to the intake pressure
Pamb upstream of the intake throttle valve 19. .kappa. in Formulas
(2), (3) is the specific heat ratio.
.function..kappa..times..kappa..kappa..kappa..times..times..times..times.-
.ltoreq..kappa..kappa..kappa..times..times..times..function..times..kappa.-
.kappa..times..kappa..kappa..kappa..times..times..times..times.>.kappa.-
.kappa..kappa..times..times..times. ##EQU00002##
Therefore, the opening degree for the low opening degree control
can be set by calculating the opening degree Thr of the intake
throttle valve 19 that satisfies following Formula (4) as a
condition that makes fcom(Pim/Pamb) constant, i.e., a condition
that satisfies Formula (2) of the isentropic flow.
<.kappa..kappa..kappa..times..times..times. ##EQU00003##
The intake air quantity is sensed with the airflow meter 23 during
the execution of the low opening degree control for controlling the
opening degree Thr of the intake throttle valve 19 to the opening
degree for the low opening degree control. Based on the intake air
quantity sensed with the airflow meter 23, the leak air quantity
Qleak at the time when the intake throttle valve 19 is fully closed
is calculated.
Thus, the passing air quantity Gath corresponding to the opening
degree Thr of the intake throttle valve 19 during the low opening
degree control can be sensed by sensing the intake air quantity
with the airflow meter 23 during the low opening degree control.
During the low opening degree control, the passing air quantity
Gath changes in accordance with the opening degree of the intake
throttle valve 19, without being affected by the pressure
difference between the pressure upstream of the intake throttle
valve 19 and the pressure downstream of the intake throttle valve
19. Therefore, by using a map or the like beforehand storing the
relationship between the opening degree of the intake throttle
valve 19 and the passing air quantity Gath during the low opening
degree control, the leak air quantity Qleak as the passing air
quantity Gath at the time when the intake throttle valve 19 is
fully closed can be calculated with high accuracy from the intake
air quantity sensed with the airflow meter 23 during the low
opening degree control, i.e., the passing air quantity Gath
corresponding to the opening degree Thr of the intake throttle
valve 19 for the low opening degree control.
Furthermore, the ECU 28 executes an ISC (idling speed control)
feedback correction amount calculation program shown in FIG. 7 to
calculate an ISC feedback correction amount ISCI for conforming
actual engine rotation speed to target idle speed when a
predetermined ISC execution condition is satisfied. The ECU 28
controls the motor 21 of the intake throttle valve 19 with the use
of the ISC feedback correction amount ISCI to perform ISC (idle
speed control) for feedback-controlling the opening degree Thr of
the intake throttle valve 19.
The ECU 28 corrects an integration amount .DELTA.I (feedback gain
of ISC) of the ISC feedback correction amount ISCI in accordance
with the leak air quantity Qleak of the intake throttle valve 19 to
correct the opening degree Thr of the intake throttle valve 19 in
accordance with the leak air quantity Qleak of the intake throttle
valve 19. Thus, the change in the relationship between the opening
degree Thr of the intake throttle valve 19 and the passing air
quantity Gath (change characteristic of passing air quantity Gath
with respect to opening degree Thr of intake throttle valve 19) due
to the change of the leak air quantity Qleak of the intake throttle
valve 19 is compensated to improve stability of the idle speed.
Next, contents of processing of the leak air quantity calculation
program of FIG. 6 and the ISC feedback correction amount
calculation program of FIG. 7 executed by the ECU 28 will be
explained. The leak air quantity calculation program shown in FIG.
6 is executed in a predetermined cycle while the ECU 28 is
energized. If the program is started, first, S101 determines
whether the engine start is in progress. If S101 is YES, the
processing proceeds to S102. S102 determines whether the present
time is in the first intake stroke period since the engine start is
commenced until the first intake strokes of the respective
cylinders are completed.
If S102 is YES, the processing proceeds to S103 to set the target
opening degree TThr of the intake throttle valve 19 at the opening
degree LThr for the low opening degree control. The opening degree
LThr for the low opening degree control is the opening degree Thr
with which the intake pressure downstream of the intake throttle
valve 19 becomes the pressure equal to or lower than the critical
pressure CP with respect to the intake pressure upstream of the
intake throttle valve 19 (i.e., pressure at which passing air
quantity Gath changes in accordance with opening degree of intake
throttle valve 19 without being affected by pressure difference
between pressure upstream of intake throttle valve 19 and pressure
downstream of intake throttle valve 19) during the intake stroke of
each cylinder.
S103 sets the target opening degree TThr of the intake throttle
valve 19 at the opening degree LThr for the low opening degree
control to control the actual opening degree Thr of the intake
throttle valve 19 to the opening degree LThr for the low opening
degree control (target opening degree TThr). Thus, the low opening
degree control for controlling the opening degree of the intake
throttle valve 19 so that the intake pressure downstream of the
intake throttle valve 19 becomes the pressure equal to or lower
than the critical pressure CP with respect to the intake pressure
upstream of the intake throttle valve 19 in the intake stroke of
each cylinder is performed.
Then, the processing proceeds to S104 to read the intake air
quantity Qafm, the engine rotation speed Ne, the coolant
temperature Tw and the actual opening degree Thr of the intake
throttle valve 19 sensed with the airflow meter 23, the crank angle
sensor 26, the coolant temperature sensor 25 and the intake
throttle valve opening degree sensor 29 during the low opening
degree control, and the like.
Then, the processing proceeds to S105 to calculate a basic leak air
quantity Qleakbse at the time when the intake throttle valve 19 is
fully closed in accordance with the intake air quantity Qafm and
the actual opening degree Thr of the intake throttle valve 19 of
the present time (i.e., during low opening degree control) with
reference to a map of the basic leak air quantity Qleakbse shown in
FIG. 8. The map of the basic leak air quantity Qleakbse shown in
FIG. 8 is set based on the relationship (in range C shown in FIG.
9) between the opening degree Thr of the intake throttle valve 19
and the passing air quantity Gath during the low opening degree
control (i.e., in state where passing air quantity Gath changes in
accordance with opening degree of intake throttle valve 19 without
being affected by pressure difference between pressure upstream of
intake throttle valve 19 and pressure downstream of intake throttle
valve 19) beforehand obtained based on test data, design data and
the like. For example, the map of the basic leak air quantity
Qleakbse is set such that the basic leak air quantity Qleakbse
increases as the intake air quantity Qafm during the low opening
degree control increases and the basic leak air quantity Qleakbse
increases as the actual opening degree Thr of the intake throttle
valve 19 during the low opening degree control decreases.
Then, the processing proceeds to S106 to calculate a correction
coefficient Cne corresponding to the engine rotation speed Ne and
the coolant temperature Tw with reference to a map of the
correction coefficient Cne (not shown). The map of the correction
coefficient Cne is set based on the relationship between the engine
rotation speed Ne and the leak air quantity Qleak at the time when
the intake throttle valve 19 is fully closed and the relationship
between the coolant temperature Tw and the leak air quantity Qleak
at the time when the intake throttle valve 19 is fully closed,
which are beforehand obtained based on test data, design data and
the like.
Then, the processing proceeds to S107 to calculate the leak air
quantity Qleak at the time when the intake throttle valve 19 is
fully closed by multiplying the basic leak air quantity Qleakbse at
the time when the intake throttle valve 19 is fully closed by the
correction coefficient Cne (i.e., Qleak=Qleakbse.times.Cne).
Then, the processing proceeds to S108. S108 updates the learning
value of the leak air quantity Qleak in a learning area
corresponding to the coolant temperature Tw as of the calculation
of the present leak air quantity Qleak with the presently
calculated leak air quantity Qleak and stores the learning value in
a rewritable nonvolatile memory such as a backup RAM (not shown) of
the ECU 28.
The ISC feedback correction amount calculation program shown in
FIG. 7 is executed in a predetermined cycle while the ECU 28 is
energized. If the program is started, S201 first determines whether
the ISC execution condition is satisfied, for example, based on
whether all conditions including a condition that the intake
throttle valve 19 is fully closed, a condition that vehicle speed
is equal to or lower than a predetermined value and a condition
that the engine rotation speed Ne is within a predetermined range
are satisfied.
If S201 determines that the ISC execution condition is satisfied,
the processing proceeds to S202 to read the actual engine rotation
speed Ne sensed with the crank angle sensor 26. Then, the
processing proceeds to S203 to calculate target idle speed Ns
corresponding to the present coolant temperature Tw with reference
to a map of the target idle speed Ns (not shown).
Then, the processing proceeds to S204 to correct the integration
amount .DELTA.I of the ISC feedback correction amount ISCI in
accordance with the leak air quantity Qleak at the time when the
intake throttle valve 19 is fully closed. In this case, the
integration amount .DELTA.I is corrected to correct the change in
the relationship between the opening degree Thr of the intake
throttle valve 19 and the passing air quantity Gath (change
characteristic of passing air quantity with respect to opening
degree Thr of intake throttle valve) due to the change of the leak
air quantity Qleak of the intake throttle valve 19.
Then, the processing proceeds to S205 to compare the actual engine
rotation speed Ne and the target idle speed Ns. If it is determined
that the actual engine rotation speed Ne is lower than the target
idle speed Ns, the processing proceeds to S206 to perform the
correction for increasing the ISC feedback correction amount ISCI
by the integration amount .DELTA.I (i.e., ISCI=ISCI+.DELTA.I).
If it is determined that the actual engine rotation speed Ne is
higher than the target idle speed Ns, the processing proceeds to
S207 to perform correction for decreasing the ISC feedback
correction amount ISCI by the integration amount .DELTA.I (i.e.,
ISCI=ISCI-.DELTA.I).
The above-described first embodiment performs the low opening
degree control for controlling the opening degree of the intake
throttle valve 19 to the fully closed position or the proximity of
the fully closed position during the first intake stroke period
since the engine start is commenced until the first intake strokes
of the respective cylinders are completed. Thus, the intake
pressure downstream of the intake throttle valve 19 is brought to
the pressure equal to or lower than the critical pressure with
respect to the intake pressure upstream of the intake throttle
valve 19, i.e., the pressure at which the passing air quantity
changes in accordance with the opening degree of the intake
throttle valve 19 without being affected by the pressure difference
between the pressure upstream of the intake throttle valve 19 and
the pressure downstream of the intake throttle valve 19. The leak
air quantity as the passing air quantity at the time when the
intake throttle valve 19 is fully closed is calculated based on the
intake air quantity sensed with the airflow meter 23 during the low
opening degree control (i.e., passing air quantity corresponding to
opening degree of intake throttle valve 19 during low opening
degree control) and the opening degree of the intake throttle valve
19. Accordingly, the leak air quantity of the intake throttle valve
19 can be calculated with high accuracy.
The air is stored in the intake passage downstream of the intake
throttle valve 19 before the first intake stroke of each cylinder
ends after the engine start is commenced. Therefore, even if the
low opening degree control for controlling the opening degree of
the intake throttle valve 19 to the fully closed position or the
proximity of the fully closed position is performed during the
first intake stroke period since the engine start is commenced
until the first intake strokes of the cylinders are completed, the
air necessary for the combustion in the engine start can be
suctioned into the cylinders, inhibiting adverse effect on the
starting performance of the engine 11.
The first embodiment corrects the integration amount .DELTA.I of
the ISC feedback correction amount ISCI in accordance with the leak
air quantity of the intake throttle valve 19 during the idle
operation to correct the opening degree Thr of the intake throttle
valve 19 in accordance with the leak air quantity of the intake
throttle valve 19. Thus, the change in the relationship between the
opening degree Thr of the intake throttle valve 19 and the passing
air quantity Gath (change characteristic of passing air quantity
Gath with respect to opening degree Thr of intake throttle valve)
due to the change in the leak air quantity Qleak of the intake
throttle valve 19 is compensated. Accordingly, the controllability
of the intake air quantity through the opening degree control of
the intake throttle valve 19 can be improved and the stability of
the idle speed can be improved without being affected by the aging
change of the leak air quantity of the intake throttle valve 19 and
the like.
Furthermore, in the first embodiment, the leak air quantity of the
intake throttle valve 19 can be calculated when the engine 11 is
started. Therefore, the correction of the opening degree of the
intake throttle valve 19 according to the leak air quantity of the
intake throttle valve 19 can be started immediately after the
engine start. As a result, the controllability of the intake air
quantity can be improved even immediately after the engine
start.
Next, a second embodiment of the present invention will be
explained in reference to FIGS. 10 and 11. In the second
embodiment, a leak air quantity calculation program shown in FIG.
11 is executed to perform low opening degree control for
controlling the opening degree of the intake throttle valve 19 to
the fully closed position or proximity of the fully closed position
during fuel cut control for suspending the fuel injection of the
engine 11 as shown in a time chart of FIG. 10. Thus, the intake
pressure downstream of the intake throttle valve 19 is brought to
pressure that is equal to or lower than the critical pressure with
respect to the intake pressure upstream of the intake throttle
valve 19 and that does not cause oil loss via valve guides in the
intake stroke of each cylinder. FC in FIG. 10 represents a fuel cut
control execution flag. The leak air quantity Qleak at the time
when the intake throttle valve 19 is fully closed is calculated
based on the intake air quantity Qafm sensed with the airflow meter
23 during the low opening degree control.
In the leak air quantity calculation program shown in FIG. 11, S301
first determines whether the fuel cut control is in progress. If
S301 is YES, the processing proceeds to S302 to set the target
opening degree TThr of the intake throttle valve 19 to the opening
degree LThr for the low opening degree control. The opening degree
LThr for the low opening degree control is the opening degree that
brings the intake pressure downstream of the intake throttle valve
19 to the pressure that is equal to or lower than the critical
pressure CP (i.e., pressure at which passing air quantity changes
in accordance with opening degree of intake throttle valve 19
without being affected by pressure difference between pressure
upstream of intake throttle valve 19 and pressure downstream of the
intake throttle valve 19) with respect to the intake pressure
upstream of the intake throttle valve 19 and that is equal to or
higher than lower limit pressure LLP for preventing the oil loss
via the valve guides during the intake stroke of each cylinder.
S302 sets the target opening degree TThr of the intake throttle
valve 19 to the opening degree LThr for the low opening degree
control to control the actual opening degree Thr of the intake
throttle valve 19 to the opening degree LThr for low opening degree
control (target opening degree TThr). Thus, the low opening degree
control for controlling the opening degree Thr of the intake
throttle valve 19 so that the intake pressure downstream of the
intake throttle valve 19 becomes the pressure that is equal to or
lower than the critical pressure CP with respect to the intake
pressure upstream of the intake throttle valve 19 and that is equal
to or higher than the lower limit pressure LLP for preventing the
oil loss via the valve guides during the intake stroke of each
cylinder is performed.
Then, S303 reads the intake air quantity Qafm, the engine rotation
speed Ne, the coolant temperature Tw, the actual opening degree Thr
of the intake throttle valve 19 and the like, which are sensed
during the low opening degree control. Then, with reference to the
map of the basic leak air quantity Qleakbse shown in FIG. 8, S304
calculates the basic leak air quantity Qleakbse at the time when
the intake throttle valve 19 is fully closed in accordance with the
intake air quantity Qafm and the actual opening degree Thr of the
intake throttle valve 19 at the present time (i.e., during low
opening degree control). S305 calculates the correction coefficient
Cne corresponding to the engine rotation speed Ne and the coolant
temperature Tw with reference to the map of the correction
coefficient Cne (not shown).
Then, S306 calculates the leak air quantity Qleak at the time when
the intake throttle valve 19 is fully closed by multiplying the
basic leak air quantity Qleakbse at the time when the intake
throttle valve 19 is fully closed by the correction coefficient
Cne. Then, S307 updates the learning value of the leak air quantity
Qleak in the learning area corresponding to the coolant temperature
Tw as of the present calculation of the leak air quantity Qleak
with the presently calculated leak air quantity Qleak and stores
the learning value in the rewritable nonvolatile memory.
The capacity of the intake passage downstream of the intake
throttle valve 19 is small in the system having the intake throttle
valves 19 in the intake manifolds 14 of the respective cylinders of
the engine 11. Therefore, if the intake throttle valve 19 is fully
closed during the fuel cut control (i.e., when rotation speed of
engine 11 is equal to or greater than predetermined value), there
is a possibility that the intake pressure downstream of the intake
throttle valve 19 declines greatly and the oil loss via the valve
guides occurs.
Therefore, the second embodiment performs the low opening degree
control for controlling the opening degree of the intake throttle
valve 19 to the fully closed position or the proximity of the fully
closed position during the fuel cut control so that the intake
pressure downstream of the intake throttle valve 19 becomes the
pressure that is equal to or lower than the critical pressure with
respect to the intake pressure upstream of the intake throttle
valve 19 and that does not cause the oil loss via the valve guides.
The leak air quantity at the time when the intake throttle valve 19
is fully closed is calculated based on the intake air quantity
sensed with the airflow meter 23 during the low opening degree
control. Accordingly, the leak air quantity of the intake throttle
valve 19 can be calculated with high accuracy while preventing the
oil loss via the valve guides and the adverse effect on the
operation of the engine 11.
In the first and second embodiments, the basic leak air quantity
Qleakbse is calculated in accordance with the intake air quantity
Qafm and the actual opening degree Thr of the intake throttle valve
19 as of the low opening degree control. Alternatively, the basic
leak air quantity Qleakbse may be calculated in accordance with the
intake air quantity Qafm and the target opening degree TThr (i.e.,
opening degree LThr for low opening degree control) of the intake
throttle valve 19 as of the low opening degree control.
In the first and second embodiments, the integration amount
.DELTA.I of the ISC feedback correction amount ISCI is corrected in
accordance with the leak air quantity of the intake throttle valve
19 during the idle operation. Alternatively, the opening degree of
the intake throttle valve 19 may be corrected in accordance with
the leak air quantity Qleak of the intake throttle valve 19 during
normal operation other than the idle operation. Thus, the change in
the relationship between the opening degree Thr of the intake
throttle valve 19 and the passing air quantity Gath (change
characteristic of passing air quantity Gath with respect to opening
degree Thr of intake throttle valve) due to the change in the leak
air quantity of the intake throttle valve 19 may be
compensated.
Next, a third embodiment of the present invention will be
explained. First, an outline of an engine intake system will be
explained in reference to FIG. 12. The inline four-cylinder engine
11 as an internal combustion engine has four cylinders of a first
cylinder #1 to a fourth cylinder #4. A surge tank 13 is provided to
an intake pipe 12 of the engine 11. Intake manifolds 14 for
introducing air into respective cylinders of the engine 11 are
provided to the surge tank 13. Intake throttle valve units 15 are
attached to the intake manifolds 14 of the respective cylinders.
Injectors (not shown) for injecting fuel are provided near intake
ports of the respective cylinders. Spark plugs (not shown) are
attached to a cylinder head of the engine 11 for the respective
cylinders. Fuel-air mixture in the cylinders is ignited with spark
discharge from the respective spark plugs. An EGR valve 30 (exhaust
gas recirculation adjustment device) that adjusts an EGR quantity
(quantity of exhaust gas recirculation quantity) is provided in an
EGR pipe (not shown) for recirculating part of exhaust gas of the
engine 11 to the intake air side.
A coolant temperature sensor 25 for sensing coolant temperature Tw
and a crank angle sensor 26 for outputting a pulse signal every
time a crankshaft of the engine 11 rotates by a predetermined crank
angle are attached to a cylinder block of the engine 11. The crank
angle CA and engine rotation speed Ne are sensed based on the
output signal of the crank angle sensor 26. Furthermore, an
accelerator operation amount ACCP (depressed amount of accelerator)
is sensed with an accelerator sensor 27.
A variation is caused among the intake air quantities of the
cylinders if the leak air quantities of the intake throttle valves
19 provided in the intake manifolds 14 of the respective cylinders
(air quantities passing through small gaps between intake throttle
valves 19 and intake passage inner wall faces when intake throttle
valves 19 are fully closed) vary among the cylinders due to
manufacture tolerances, aging changes, and the like. Therefore,
there is a possibility that the torque of the respective cylinders
varies and the engine rotation speed fluctuates largely.
As a countermeasure, the ECU 28 executes an each cylinder intake
throttle valve opening degree correction program shown in FIG. 14
to perform each cylinder intake throttle valve opening degree
correction for correcting the opening degree of the intake throttle
valve 19 in accordance with the leak air quantity of each cylinder
as follows.
If the leak air quantity of the intake throttle valve 19 increases
when the intake throttle valve 19 has a function to generate an
airflow current (e.g., tumble flow or swirl flow) for equalizing
the fuel-air mixture, the intensity of the airflow generated by the
intake throttle valve 19 is weakened correspondingly, and the
effect to equalize the fuel-air mixture is lowered. Therefore, if
the EGR quantity is increased during the low load operation of the
engine 11, in which the influence of the EGR is large, as shown by
a solid line "a" in a time chart of FIG. 13, the effect of
equalizing the fuel-air mixture is further lowered by the influence
of the EGR in the cylinder (for example, second cylinder #2)
causing the large leak air quantity of the intake throttle valve
19. As a result, the combustion state becomes unstable and the
rotation speed corresponding to the combustion stroke falls greatly
over a normal variation range .DELTA.Ne(nor). A broken line "b" in
FIG. 13 shows the rotation speed Ne in the case where the airflow
control function is not provided.
Paying attention to such the characteristic, in the present
embodiment, first, EGR increase control for controlling the EGR
valve 30 to increase the EGR quantity during the low load operation
of the engine 11 is performed. The rotation fluctuation due to the
combustion in the respective cylinders is sensed as a parameter for
evaluating the combustion states of the respective cylinders during
the EGR increase control, and the cylinder causing an unstable
combustion state is determined based on the rotation fluctuation
due to the combustion in the respective cylinders. The cylinder
causing the unstable combustion state is determined to be a large
leak air cylinder (cylinder causing large leak air quantity).
For example, as shown in the time chart of FIG. 13, the maximum
values (peak values) of the rotation speed Ne corresponding to the
combustion strokes of the respective cylinders (first cylinder #1
to fourth cylinder #4) are calculated as the rotation speeds
Ne(#1)-Ne(#4) of the respective cylinders #1-#4 during the EGR
increase control. Then, average rotation speed Ne(av) of all the
cylinders is calculated from the rotation speeds Ne(#1)-Ne(#4) of
the respective cylinders. Then, deviations between the average
rotation speed Ne(av) of all the cylinders and the rotation speeds
Ne(#1)-Ne(#4) of the respective cylinders are calculated. Thus,
rotation fluctuation amounts .DELTA.Ne(#1)-.DELTA.Ne(#4) of the
respective cylinders toward the lower rotation speed from the
average rotation speed Ne(av) of all the cylinders are calculated
(i.e., .DELTA.Ne(#i)=Ne(av)-Ne(#i), i=1 to 4)
Then, the maximum rotation fluctuation amount .DELTA.Ne(max) is
determined out of the rotation fluctuation amounts
.DELTA.Ne(#1)-.DELTA.Ne(#4) of the respective cylinders in a
predetermined period (period D shown in FIG. 13, for example,
period of 720.degree. CA). If the maximum rotation fluctuation
amount .DELTA.Ne(max) is equal to or greater than a predetermined
value .alpha., it is determined that the cylinder corresponding to
the maximum rotation fluctuation amount .DELTA.Ne(max) is the large
leak air cylinder. That is, in the cylinder causing the large leak
air quantity, the combustion state becomes unstable during the EGR
increase control, and the rotation speed falls greatly over the
normal variation range .DELTA.Ne(nor). Therefore, the cylinder
causing the rotation fluctuation amount .DELTA.Ne that is directed
toward the lower rotation speed from the average rotation speed
Ne(av) of all the cylinders and that is equal to or greater than
the predetermined value .alpha. is determined to be the large leak
air cylinder.
Then, the opening degree Thr of the intake throttle valve 19 is
corrected in accordance with the maximum rotation fluctuation
amount .DELTA.Ne(max) reflecting the leak air quantity of the
intake throttle valve 19 of the large leak air cylinder during a
period (period E, in FIG. 13) corresponding to the intake stroke of
the large leak air cylinder. Thus, the opening degree Thr of the
intake throttle valve 19 is corrected in accordance with the leak
air quantity of the intake throttle valve 19 of the large leak air
cylinder.
By repeatedly performing the processing of sensing the rotation
fluctuations of the respective cylinders during the EGR increase
control, the processing of determining the large leak air cylinder
based on the rotation fluctuations of the respective cylinders, and
the processing of correcting the opening degree Thr of the intake
throttle valve 19 in the period corresponding to the intake stroke
of the large leak air cylinder, the variation among the intake air
quantities due to the variation among the leak air quantities of
the intake throttle valves 19 of the respective cylinders is
corrected with high accuracy. Thus, the engine rotation fluctuation
due to the variation among the leak air quantities of the intake
throttle valves 19 of the respective cylinders is inhibited.
Next, the contents of processing of the each cylinder intake
throttle valve opening degree correction program shown in FIG. 14
executed by the ECU 28 will be explained. The each cylinder intake
throttle valve opening degree correction program shown in FIG. 14
is executed in a predetermined cycle while the ECU 28 is energized.
If the program is started, S401 first determines whether the low
load operation of the engine 11 is in progress. If S401 is YES, the
processing proceeds to S402 to perform the EGR increase control for
controlling the EGR valve 30 such that the EGR quantity
increases.
Then, the processing proceeds to S403 to determine whether the EGR
quantities of all the cylinders have increased, for example, based
on whether a predetermined period necessary for the EGR quantities
of all the cylinders to increase has elapsed. If it is determined
that the EGR quantities of all the cylinders have increased, the
processing proceeds to S404 to calculate the maximum values (peak
values) of the rotation speed Ne corresponding to the combustion
strokes of the respective cylinders as the rotation speeds
Ne(#1)-Ne(#4) of the respective cylinders based on the output of
the crank angle sensor 26 during the EGR increase control. Then,
the processing proceeds to Step S405 to calculate the average
rotation speed Ne(av) of all the cylinders from the rotation speeds
Ne(#1)-Ne(#4) of the respective cylinders.
Then, the processing proceeds to S406. S406 calculates the
deviations between the average rotation speed Ne(av) of all the
cylinders and the rotation speeds Ne(#1)-Ne(#4) of the respective
cylinders as the rotation fluctuation amounts
.DELTA.Ne(#1)-.DELTA.Ne(#4) of the respective cylinders toward the
lower rotation speed from the average rotation speed Ne(av) of all
the cylinders (i.e., .DELTA.Ne(#i)=Ne(av)-Ne(#i), i=1 to 4).
Then, the processing proceeds to S407 to determine the maximum
rotation fluctuation amount .DELTA.Ne(max) out of the rotation
fluctuation amounts .DELTA.Ne(#1)-.DELTA.Ne(#4) of the respective
cylinders in the predetermined period (for example, period of
720.degree. CA). Then, the processing proceeds to S408 to determine
whether the maximum rotation fluctuation amount .DELTA.Ne(max) is
equal to or greater than the predetermined value .alpha..
If S408 determines that the maximum rotation fluctuation amount
.DELTA.Ne(max) is smaller than the predetermined value .alpha., the
maximum rotation fluctuation amount .DELTA.Ne(max) is within the
normal variation range .DELTA.Ne(nor). Therefore, the cylinder
corresponding to the maximum rotation fluctuation amount
.DELTA.Ne(max) is determined not to be the large leak air cylinder,
and the program is ended.
If S408 determines that the maximum rotation fluctuation amount
.DELTA.Ne(max) is equal to or greater than the predetermined value
.alpha., the maximum rotation fluctuation amount .DELTA.Ne(max)
exceeds the normal variation range .DELTA.Ne(nor). In this case,
the processing proceeds to S409 to determine that the cylinder
corresponding to the maximum rotation fluctuation amount
.DELTA.Ne(max) is the large leak air cylinder. Then, the processing
proceeds to S410 to correct the opening degree of the intake
throttle valve 19 in the period corresponding to the intake stroke
of the large leak air cylinder in accordance with the maximum
rotation fluctuation amount .DELTA.Ne(max) reflecting the leak air
quantity of the intake throttle valve 19 of the large leak air
cylinder. Thus, the opening degree of the intake throttle valve 19
is corrected in accordance with the leak air quantity of the intake
throttle valve 19 of the large leak air cylinder. In this case, the
opening degree of the intake throttle valve 19 is corrected such
that the variation among the intake air quantities due to the
variation among the leak air quantities is corrected.
By repeatedly executing the program, the variation among the intake
air quantities due to the variation among the leak air quantities
of the intake throttle valves 19 of the respective cylinders is
corrected with high accuracy. As a result, the engine rotation
fluctuation due to the variation among the leak air quantities of
the intake throttle valves 19 of the respective cylinders is
inhibited.
In the above-described third embodiment, attention is paid to the
phenomenon that, if the EGR quantity is increased during the low
load operation of the engine 11, the combustion state in the
cylinder causing the large leak air quantity of the intake throttle
valve 19 becomes unstable due to the influence of the EGR and the
rotation speed corresponding to the combustion stroke of the
cylinder falls greatly. In the third embodiment, the rotation
fluctuation amounts .DELTA.Ne(#1)-.DELTA.Ne(#4) of the respective
cylinders toward the lower rotation speed from the average rotation
speed Ne(av) of all the cylinders are calculated during the EGR
increase control for increasing the EGR quantity during the low
load operation of the engine. The cylinder corresponding to the
maximum rotation fluctuation amount .DELTA.Ne(max) is determined to
be the large leak air cylinder. The opening degree of the intake
throttle valve 19 is corrected in accordance with the maximum
rotation fluctuation amount .DELTA.Ne(max) reflecting the leak air
quantity of the intake throttle valve 19 of the large leak air
cylinder during the period corresponding to the intake stroke of
the large leak air cylinder. Thus, the opening degree of the intake
throttle valve 19 is corrected in accordance with the leak air
quantity of the intake throttle valve 19 of the large leak air
cylinder.
By repeatedly executing these processings, the variation among the
intake air quantities due to the variation among the leak air
quantities of the intake throttle valves 19 of the respective
cylinders can be corrected with high accuracy. Thus, the engine
rotation fluctuation due to the variation among the leak air
quantities of the intake throttle valves 19 of the respective
cylinders can be inhibited, and the stability of the idle speed can
be improved during the idle operation.
Moreover, there is no need to provide the bypass passages bypassing
the intake throttle valves 19 of the respective cylinders or the
control valves that open and close the bypass passages. Therefore,
the system structure can be simplified and the cost can be reduced.
The present invention may be applied to the system having the
bypass passages bypassing the intake throttle valves 19 in the
intake manifolds 14 of the respective cylinders and the control
valves in the bypass passages of the respective cylinders for
opening/closing the bypass passages respectively.
The maximum rotation fluctuation amount .DELTA.Ne(max) exceeds the
normal variation range .DELTA.Ne(nor) when the maximum rotation
fluctuation amount .DELTA.Ne(max) is greater than the predetermined
value .alpha.. Therefore, in the present embodiment, it is
determined that the cylinder corresponding to the maximum rotation
fluctuation amount .DELTA.Ne(max) is the large leak air cylinder.
When the maximum rotation fluctuation amount .DELTA.Ne(max) is
smaller than the predetermined value .alpha., the maximum rotation
fluctuation amount .DELTA.Ne(max) is within the normal variation
range .DELTA.Ne(nor). In this case, it is determined that the
cylinder corresponding to the maximum rotation fluctuation amount
.DELTA.Ne(max) is not the large leak air cylinder. Thus, erroneous
determination that the cylinder causing the rotation speed slightly
lower than the average rotation speed is the large leak air
cylinder can be precluded.
In the third embodiment, it is determined that the cylinder causing
the largest rotation fluctuation amount toward the lower rotation
speed from the average rotation speed of all the cylinders during
the EGR increase control is the large leak air cylinder.
Alternatively, it may be determined that the cylinder causing the
largest rotation fluctuation amount between the time before the EGR
increase control is performed and the time when the EGR increase
control is performed is the large leak air cylinder.
In the third embodiment, the EGR increase control for increasing
the external EGR quantity by controlling the EGR valve 30 is
performed. In a system having a variable valve timing device that
changes valve timing of the intake valve or the exhaust valve, the
EGR increase control for increasing an internal EGR quantity by
controlling a valve overlap amount between the intake valve and the
exhaust valve may be performed.
In the first to third embodiments, the present invention is applied
to the four-cylinder engine. Alternatively, the present invention
may be applied to a two-cylinder engine, a three-cylinder engine,
or an engine having five or more cylinders.
In the first to third embodiments, the present invention is applied
to the intake port injection engine. Alternatively, the present
invention may be applied to a direct injection engine or a dual
injection engine having injectors in both of the intake port and
the cylinder.
While the invention has been described in connection with what is
presently considered to be the most practical and preferred
embodiments, it is to be understood that the invention is not to be
limited to the disclosed embodiments, but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
* * * * *